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Walk me thru a vaccum synch?

Discussion in 'XJ Technical Chat' started by ouchie, Sep 19, 2011.

  1. ouchie

    ouchie Member

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    Okay so I am going to mount and (try) to tune my newly cleaned/rebuilt/wet float level checked and bench synched carbs tomorrow.

    In preparation for this I borrowed an older Motion Pro mercury manometer but... I really don't know exactly how to do this.

    I do know that ultimately I want all four levels to be...level ;-)

    I am guessing I need to somehow calibrate the tool before starting the test, right?

    I plan on installing my new manifolds first, then cleaning/gapping plugs.

    Then getting going with the vaccum synch.

    TIA!
     
  2. wizard

    wizard Active Member

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    It's easier if you make a cheapo clear tube job, get a piece of stick 5 foot long, enough small bore clear tube to go double up the wood & back to the vac ports, half fill the tubing with fluid (I use red auto trans fluid) fit the ends of the tubes on 1 & 2 & ballance those (caps on 3 & 4) then do 3 & 4, then 2 & 3, easy as. I put some restrictors in the tubes ( I used 2 of the hollow treaded bolts from indicators, so you get the idea) this is less complicated than a single manometer.
     
  3. MN-Maxims

    MN-Maxims St. Paul Minnesota

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  4. ouchie

    ouchie Member

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    Yep valves are adjusted ....
     
  5. MN-Maxims

    MN-Maxims St. Paul Minnesota

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    If you are useing a single car type vacuum gauge or....... ? the motion pro?
     
  6. ouchie

    ouchie Member

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    it's got 4 mercury levels and hoses.....pretty sure it's made bikes
     
  7. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    Makes it easy as possible.

    -Block off the YICS.
    -Hook up manometer to all 4 vacuum ports on the intake manifolds. (You'll need the petcock on PRI if you're using the bike's fuel tank.)
    -Set up a box fan blowing on the motor.
    -Fire up the bike. It should already be warmed up, let it warm back up all the way, and adjust the idle to around 1000~1100.
    -Look at your manometer. #3 is "home base" as it's only adjustable via the big idle knob.

    "Blip" the throttle between tweaks, and allow it to settle back down to idle.

    -Adjust #1 until it matches #2.
    -Adjust #2, it will bring #1 along, until they both match #3.
    -Adjust #4 to match #3.

    At this point they should all be making the same vacuum on the gauge; the actual reading isn't as important as matching them.

    Remove YICS tool (or homemade blockage) and re-adjust idle via main knob. I believe spec on the 650 is 1050rpm.

    Re-check/re-sync after making any major mixture adjustments.
     
  8. ouchie

    ouchie Member

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    Okey dokey, that sounds real good though it looks like i have another problem to deal with first

    I fired up the bike to let it warm up.....

    Everything went better than expected (this is my first time doing this) bike fired up pretty quick...idled around 1800...then...WHOA NELLIE!!!!!!

    Once warm she was off to the barn an' ole Newt couldn't hold her. Holy cow she was racing!

    I've let her cool down and adjusted the idle a few times...got her right around 1200 but then same thing...she starts racing either on her own or if I blip the throttle....

    Not sure where I should start looking though I can say:

    She clunked nicely
    wet float set at 3mm
    Plugs cleaned and gapped
    valves adjusted with proper shims
    new intake manifolds/gaskets
    YICs Eliminator installed
     
  9. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    BENCH SYNC first. Sounds like you're so far off one is pulling the others up. All it takes is for one to be far enough off the start lifting its slide, and the others will follow.
     
  10. ouchie

    ouchie Member

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    I knew I was forgetting to include one of the steps when I was writing that...yes, BENCH SYNCH!!! LOL

    I did, and have now determined that my bench synching skills...suck butt!

    I was out there awhile ago and staring and thinking, staring and thinking....then decided to give that big old wheel a turn or 2...basically gave it almost 1 full revolution(counterclockwise when looking at it from the rear)

    Then I backed each synch screw off 2 full turns...

    Here's what I came up with...around 1400 rpm.

    [​IMG]

    Then I fiddled a little more and got it to around a smidge over 1000 rpm...I'd guess pretty close to that 1050 you were referring to.

    Tried to use the manometer but....seems to be "out" of mercury, d'oh!

    I called the guy and he said he forgot to mention that when he was carrying it out he tipped it and I guess the vent tube wasn't closed....oops!
    Wondered why it took him so long to bring it outside ;-)


    i have some mercury and an irrigation syringe so will try in the morning to slowly add merc until it works...if not I guess I'll order one, what's another $100 at this point right?
     
  11. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    The new ones don't use mercury, they use stainless steel slugs.

    You do have to get them synchronized, or you'll have a hanging idle.
     
  12. ouchie

    ouchie Member

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    Yep...Motion Pros "new"one is mercury-less...uses another proprietary liquid...

    I am betting I'll be able to get some in this one though.

    If I do have to buy one do you recommend the stainless slug variety?
     
  13. Militant_Buddhist

    Militant_Buddhist Member

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    well they aren't as tasty for the nieces and nephews to chew on as the mercury ones....

    It may well not be your bench sync skills. ANY vacuum leak what-so-ever will throw things wildly off. With an accurate bench sync you should be able to throw the carbs on and be in closer than 1/8th turn territory.

    With a vacuum leak on the other hand you could vacuum sync them and have entire idle circuits covered by the butterfly while others are open. A hair pulling, ultimately fruitless PILE of messing around.

    Get yourself a can of ether and the red straw off some other spray can. Poke around and give it the tiniest of squirts here and there. (no need to fog the whole area and gas yourself out of the garage or worse)
     
  14. Polock

    Polock Well-Known Member

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    when you turned the sync screws 2 turns, you threw the bench sync clean out of the ball park.
    i suggest you make a two bottle sync tool, their the easiest to get a real bad sync to come in with, very little chance of sucking liquid into the motor and no restrictors needed
     

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